1. Field of the Invention
The present invention relates to a lens barrel, i.e., a thin lens barrel for use in a camera, and more particularly, to a lens barrel incorporated in a so-called lens shutter camera.
2. Description of the Related Art
Generally, a zoom lens barrel includes a stationary barrel fixed to the camera body, and one or more than movable barrels fitted inside the stationary barrel. It is necessary to increase the lens barrel moving-out amount in order to meet a demand of higher zoom ratio of the zoom lens. However, if the moving-out amount is increased by increasing the length of each movable barrels being included in the lens barrel, the length of the stationary barrel in which all the movable barrels are housed also increases. If the length of the stationary barrel increases, the length of the lens barrel that is collapsed into the camera body increases, causing the camera body to become thicker. If the moving-out amount is increased by increasing the number of movable barrels, the outer diameter of the lens barrel increases, which results in an increase in the size of the camera body. In order to resolve these problems and to achieve a higher zoom ratio zoom lens and compact camera body, various multi-step moving-out zoom lens barrels, having at least three barrels including a plurality of movable barrels which are fitted inside a stationary barrel, have been conventionally proposed, for example, in Japanese Laid-Open Patent Application Hei 7-27963.
The construction of a conventional lens barrel is explained below using a three-step moving-out lens barrel which has three movable barrels proposed in Japanese Laid-Open Patent Application Hei 7-27963. FIG. 19 is a vertical cross-sectional view outlining the construction of a lens barrel proposed in Japanese Laid-Open Patent Application Hei 7-27963. Fixed barrel 101 is mounted inside and is fixed to camera body B, and lead guide 101a is formed on the inner surface of stationary barrel 101. First rotating barrel 102 is located inside stationary barrel 101, and lead follower 102a and gear 102b are formed on the outer surface of first rotating barrel 102. Because lead follower 102a is engaged with lead guide 101a, when the rotational drive force from the drive source (not shown in the drawing) inside camera body B is transmitted to gear 102b, first rotating barrel 102 moves along optical axis AX while rotating.
First straight advancing barrel 103 is located inside first rotating barrel 102. Claws 103b are formed on the outer surface of first straight advancing barrel 103, and claws 103b are engaged with claws 102d formed on the inner surface of first rotating barrel 102 in a bayonet-connection. Pins 103c are also formed on the outer surface of first straight advancing barrel 103 and are engaged with straight advancement grooves 101b formed on the inner surface of stationary barrel 101. Therefore, when first rotating barrel 102 moves along optical axis AX while rotating, first straight advancing barrel 103 moves straight ahead along optical axis AX together with first rotating barrel 102, while being prevented from rotating by means of straight advancement grooves 101b.
Second rotating barrel 104 is located inside first straight advancing barrel 103. Cam followers 104a are located on the outer surface of second rotating barrel 104, and cam followers 104a are engaged with straight advancement grooves 102c of first rotating barrel 102 via cam holes 103d formed on first straight advancing barrel 103. Therefore, when first rotating barrel 102 rotates, its rotational force is transmitted to second rotating barrel 104 by means of cam followers 104a. Second rotating barrel 104 then moves along optical axis AX, regulated by straight advancement grooves 102c, while rotating along cam holes 103d.
Second straight advancing barrel 105 is located inside second rotating barrel 104. Claws 105b are formed on the outer surface of second straight advancing barrel 105, and claws 105b are engaged with claws 104b formed on the inner surface of second rotating barrel 104 in a bayonet-connection. Pins 105a are also formed on the outer surface of second straight advancing barrel 105, and are engaged with straight advancement grooves 103a formed on the inner surface of first straight advancing barrel 103. Therefore, when second rotating barrel 104 moves along optical axis AX while rotating, second straight advancing barrel 105 moves straight ahead along optical axis AX together with second rotating barrel 104, while being prevented from rotating by means of straight advancement grooves 103a.
Third straight advancing barrel 106 is located inside second rotating barrel 104. First block 107 is fixed and supported inside third straight advancing barrel 106. First block 107 comprises a focus unit, shutter unit, first lens unit and first lens holder to support the first lens unit, which are not shown in the drawing.
Cam followers 106a are located on the outer surface of third straight advancing barrel 106, and cam followers 106a are engaged with cam grooves 104c formed on the inner surface of second rotating barrel 104. Pins 105d are formed on the outer surface of second straight advancing barrel 105, and pins 105d are engaged with straight advancement grooves 106b formed on the inner surface of third straight advancing barrel 106. Therefore, when second rotating barrel 104 moves along optical axis AX while rotating, third straight advancing barrel 106 moves straight ahead along optical axis AX due to the movement of cam followers 106a along cam grooves 104c, while being prevented from rotating by means of straight advancement grooves 106b. When third straight advancing barrel 106 moves, second straight advancing barrel 105 enters gap 107a between third straight advancing barrel 106 and first block 107, but does not interfere with third straight advancing barrel 106 or first block 107.
Second block 108 is also located inside second straight advancing barrel 105. Second block 108 comprises a second lens unit and a second lens holder to support the second lens unit, which are not shown in the drawing. Cam followers 108a are located on the outer surface of the second lens holder, and are engaged with cam grooves 104d formed on the inner surface of second rotating barrel 104 via straight advancement grooves 105c formed on second straight advancing barrel 105. Therefore, when second rotating barrel 104 moves along optical axis AX while rotating, second block 108 moves straight ahead along optical axis AX due to the movement of cam followers 108a along cam grooves 104d, while being prevented from rotating by means of straight advancement grooves 105c.
Flexible substrate F, which electrically connects the focus unit and shutter unit comprising first block 107 and camera body B, is located inside the lens barrel. Flexible substrate F is guided by being attached to first through third straight advancing barrels 103, 105 and 106 such that it does not come near first and second rotating barrels 102 and 104. Because of this, it is not affected by the rotation of first and second rotating barrels 102 and 104. When the lens barrel moves from the telephoto condition to the wide angle condition and to the completely collapsed condition, flexible substrate F becomes loose. However, because the excess length of flexible substrate F is housed inside flexible substrate housing box 109 located on the outer surface of stationary barrel 101, the outer diameter of the lens barrel may be made smaller than when flexible substrate F is housed in the gaps between the barrels.
In the three-step moving-out lens barrel proposed in Japanese Laid Open Patent Application Hei 7-27963 described above, the movable barrels that are moved out in the first step comprise two barrels, i.e., first rotating barrel 102 and first straight advancing barrel 103, the movable barrels that are moved out in the second step comprise two barrels, i.e., second rotating barrel 104 and second straight advancing barrel 105, and the movable barrels that are moved out in the third step comprise one barrel, i.e., third straight advancing barrel 106. While the moving-out in the third step is achieved by means of second rotating barrel 104, which is located around third straight advancing barrel 106, and second straight advancing barrel 105, which is located inside third straight advancing barrel 106, the moving-out in the second step is achieved by means of two barrels, i.e., first straight advancing barrel 103 and first rotating barrel 102, which are located around second rotating barrel 104.
In order to have second straight advancing barrel 105 located inside third straight advancing barrel 106 as described above, gap 107a between first block 107 and third straight advancing barrel 106 is formed for second straight advancing barrel 105 to enter. This is realized by making the outer diameter of first block 107 small, by which the outer diameter of the part of the lens barrel that is used for the third step moving-out may be made small. Similarly, if first straight advancing barrel 103 that is used for the second step moving-out is located inside second rotating barrel 104, the diameter of the part of the lens barrel that is used for the second-step moving-out may be made smaller. However, it is difficult to obtain space to allow first straight advancing barrel 103 to be inside second rotating barrel 104 without first straight advancing barrel 103 interfering with second straight advancing barrel 105.
Japanese Laid-Open Patent Application Hei 7-128567 also proposes a three-step moving-out lens barrel that has a particular rotation transmission mechanism in order to allow high zoom ratio of the zoom lens and a compact camera body. However, in this lens barrel, the rotation transmission mechanism comprising a number of gears, pinions, etc. requires that a large space exist around the optical system in the completely collapsed condition. Consequently, the outer diameter of the lens barrel inevitably becomes large.